Exogenous carbon turnover within the soil food web strengthens soil carbon sequestration through microbial necromass accumulation

Exogenous carbon turnover within soil food web is important in determining the trade‐offs between soil organic carbon (SOC) storage and carbon emission. However, it remains largely unknown how soil food web influences carbon sequestration through mediating the dual roles of microbes as decomposers and contributors, hindering our ability to develop policies for soil carbon management. Here, we conducted a 13C‐labeled straw experiment to demonstrate how soil food web regulated the residing microbes to influence the soil carbon transformation and stabilization process after 11 years of no‐tillage. Our work demonstrated that soil fauna, as a “temporary storage container,” indirectly influenced the SOC transformation processes and mediated the SOC sequestration through feeding on soil microbes. Soil biota communities acted as both drivers of and contributors to SOC cycling, with 32.0% of exogenous carbon being stabilizing in the form of microbial necromass as “new” carbon. Additionally, the proportion of mineral‐associated organic carbon and particulate organic carbon showed that the “renewal effect” driven by the soil food web promoted the SOC to be more stable. Our study clearly illustrated that soil food web regulated the turnover of exogenous carbon inputs by and mediated soil carbon sequestration through microbial necromass accumulation. Bacterial and fungal communities constitute “production pump,” which dominated the decomposition process of exogenous organic carbon by anabolism, and made it into the “assembly line” of the new soil carbon. “Driving pump,” mainly included the higher trophic levels of the soil food web, which preferred to accelerate the microbial anabolism or turnover rate by trophic cascading effect. “Formation pump” was composed of bacterial and fungal necromass, in which microbial communities contributed to new soil carbon via accumulating anabolism‐induced necromass. Within the overall processes, the “renewal effect” driven by the soil food web promoted the SOC sequestration.